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Thread: Fast Fred's Secrets of the OMC MOD50's Thread #1

  1. #121
    YARD BIRD
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    Default fast fred :

    [QUOTE=Fast Fred]Roy, that box find ya? got the one you sent, the thing is mint, thanks


    I got it for sure ; it's fine . Hope to install it real soon. Thanks again -Roy

  2. #122
    FFX-61
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    ok ,corrected hp, thinkin takes 8hp off to get to the prop shaft with about 5ft.lb. O' torque, thay are not over a 1000ft up at the dyno so not exspectin a drop in hp thare

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    Sam Cullis Mark75H's Avatar
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    No, you are sort of mixing prop shaft hp vs powerhead hp and corrected hp .... I'm talking about the actual torque readings vs "corrected" to standard atmospheric ... sort of a "fudge factor"

    Ask for the actual dyno numbers as single dots on a graph or a list of actual torque numbers at specific rpms with no correction factor. Also ask for the barometric pressure, humidity and temperature at the beginning of the run and end. Without the conditions, the "correction factor" is meaningless (except as a "feel good" number to make you happier with spending $$$$).
    Since 1925, about 150 different racing outboards have been made.


  4. #124
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    well kinda lookin at it like this, on race day the barOmeter bein up or down
    every ones guna climb or fall by that %, on that particular Dyno thare have Been 3cly powerheads that have gone on to lay down Law in thare Class,
    thinkin thoughin Down more HP and Boot LBs than any of them, corrected or ,.
    ya maybe "feel good numbs' " the kind that make Drool run down yourface

    i'll get all that info

  5. #125
    Team Member JohnsonM50's Avatar
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    Quote Originally Posted by Fast Fred
    this is the reed blocks of the 19s
    Fred, those are 2 stage reeds ? and Im guessin at least the top is carbon fibre? Next Q is would removing or cutting back stops on metal reeds be more risky? understanding that if a metal reed lets go you got a problem but I mean likelyhood of breakeage ?

  6. #126
    Sam Cullis Mark75H's Avatar
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    Exactly correct.

    Reed stop is a misnomer, they stop harmonic vibration of the reed, not limit opening distance (on most motors). On a few motors Mercury lowered the stop height to reduce the power in a second tier motor (115 vs 135, etc), but I do not know of any other motors where the maker set them lower causing a power decrease. Generally reed stops are there to increase reed life, no other reason. If you want the reeds to break, by all means, remove the "stops"

    Boysen "Dual Stage" type reeds are their own vibration dampeners and probably don't need stops on most motors
    Since 1925, about 150 different racing outboards have been made.


  7. #127
    Administrator Ron Hill's Avatar
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    Default Does The Bottom Reed Open???

    On the two stage Boysen Reeds, does the fuel go through the reed itself and does the bottom reed ever open???

    Seems like opening the hole in the thicker reed would increase flow???

    I do know, that my dad always took the minus on a reed stop...like plue .025 minus .025..He'd go for the minus...He never believed that a reed could open and close fast enough....but he did like the reeds to seat on the blocks. There were engine builders that "pre" loaded the reeds and they never closed...bitch to start and spit gass back through the carbs...

  8. #128
    FFX-61
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    two Stinger powerheads side by side, same everything, but one with reedstops,
    one without, same load on each, ( reeds should be seated, or you are waistin power) we make a pull on each same time, reedstop moda peaks, nostop moda pulls 4-500 more rpm .

    all the reeds get openin, seems thay did add stops to the 19s powerhead,and the 31m blocks i got do have stops.

  9. #129
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    Default Mod 50

    All the 3-cylinder race engines had stops. Mark 75 is correct on the function of the reed stop. Stop height and shape are very important. Early M50 engines used 0.010" thick stainless steel reeds, each reed was measured. Reeds which measured 0.0098" would break, reeds which measured 0.0102" would never break. We always used 0.0100/0.0102. We went to Boyensen reeds once we found a design which made more power than the steel reeds. Did a lot of work with Eyvind to find materials and upper/lower thickness which would work. Power on the engines got better over the years, Tradewinds 19S made 95hp at the propshaft, M31 was in the high 120's at the propshaft. The only way to compare day to day tests is to use corrected numbers. True, on race day everyone sees the same weather conditions, but for development you have to correct.

  10. #130
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    talked to Mike about corrected numbers , said the computor corrects the atmosphere data at the time of the pull to the national bace line.

    can you tell us about secandary 2bbl carbs, did they make a set of 1 1/4" with secandarys?
    thanks
    FF

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